1. Field of the Invention
The present invention relates to a method and apparatus for treating wastes by gasification, and more particularly to a method and apparatus for treating wastes by gasification at a relatively low temperature and then at a relatively high temperature to recover metals or ash content in the wastes in such a state that they can be recycled, and gases containing carbon monoxide (CO) and hydrogen (H.sub.2) for use as synthesis gas of ammonia (NH.sub.3).
2. Description of the Prior Art
Ammonia (NH.sub.3) is a basic material for chemical industries and is mass-produced for use in production of nitric acid, various fertilizers; including ammonium nitrate, ammonium sulfate and urea; acrylonitrile, caprolactam or the like. Ammonia is synthesized from nitrogen (N.sub.2) and hydrogen (H.sub.2) under a high pressure in the presence of a catalyst. Hydrogen (H.sub.2) has been produced by either steam reforming of natural gas or naphtha, or partial combustion, i.e. gasification, of hydrocarbon such as petroleum, coal or petroleum coke.
It has heretofore been customary to treat organic wastes including municipal wastes, plastic wastes including fiber-reinforced plastics (FRP), biomass wastes, and automobile wastes by incineration to reduce the volume thereof, or to discard the organic wastes in an untreated state in landfill sites.
Therefore, a small quantity of useful resources has been recovered from the organic wastes and used for recycling, irrespective of direct or indirect utilization.
Hydrogen which is a material for ammonia (NH.sub.3) is obtained from natural gas, naphtha, petroleum, coal or petroleum coke. Since most of those materials are dependent on importation from abroad, there has long been a need for a way of procuring materials which are inexpensive and available locally.
On the other hand, the incineration of solid wastes has been disadvantageous for the following reasons:
A stoker furnace or a fluidized-bed furnace has heretofore been used for the incineration of solid wastes. However, this incineration has been problematic with respect to environmental conservation, or recycling of resources or energy. To be more specific, large quantities of exhaust gas are discharged because of high air ratio, and toxic Dioxins are contained in the exhaust gas. Further, metals which are discharged from the furnace are not suitable for recycling because they are oxidized, and landfill sites become more scarce year by year. Recently, the number of waste treatment facilities which incorporate ash-melting equipment is increasing, however, a problem is encountered in construction cost and/or operating cost of such waste treatment facilities. Further, recently, there has been developing a tendency to utilize energy of solid wastes efficiently.
Dumping solid wastes in an untreated state on the land has become more difficult because of scarcity of landfill sites, and has not been allowable from the viewpoint of environmental conservation. Therefore, there is no site where solid wastes such as shredder dust of scrapped cars can be disposed of.